A ceramic heater for a glow plug is made of a conductive ceramic material of a conductor and an insulating ceramic material of a ceramic base. The conductor is formed of a heating element and a lead, and the materials of the heating element and the lead are selected and the shapes thereof are designed in such a manner that a resistance value of the lead is less than that of the heating element.
In recent years, there has been a demand for a heater, the temperature of which can be increased very quickly. For this reason, it is necessary to apply a voltage to the heating element higher than an applied voltage in the related art, and to allow high current to flow through the heating element. However, when high current flows through the heating element, parts of the heater may generate a locally large amount of heat, and thereby high thermal expansion may occur locally. As a result, there is a problem in that high thermal stress may occur locally, and the durability of the heater may decrease.